Most Common Mistakes When Declaring Cryptocurrencies to the Tax Agency (and How to Avoid Them)

The complexity of the crypto ecosystem and the lack of uniform criteria make declaring cryptocurrencies to the AEAT a process prone to mistakes. Thousands of investors use incomplete data or automatic reports without review, which can result in tax discrepancies.

The most common issue is lack of traceability: movements between wallets, swaps, and DeFi operations are not always recorded correctly. Without professional review, it’s easy to omit transactions or duplicate records, directly affecting your income tax results.

Declaring cryptocurrencies is not like declaring traditional stocks or investment funds. The crypto ecosystem presents unique challenges:

• Multiple wallets and exchanges: Most investors hold cryptocurrencies across several platforms
• Complex operations: Staking, farming, airdrops, NFTs — each has different tax treatment
• Lack of official reports: Unlike banks, exchanges don’t always provide tax certificates
• Cross-chain movements: Bridges and conversions complicate traceability
• Tokens without market value: Many received tokens have no official price at the time of the transaction

Moreover, tax regulations evolve constantly, and what was valid a year ago may not be now. The AEAT regularly updates its criteria, and staying current requires specialized knowledge.

These are the 6 most common mistakes we detect when reviewing cryptocurrency tax reports:

1. Failing to include crypto-to-crypto exchanges, assuming only conversions to euros must be declared.

2. Confusing internal wallet transfers with real sales or swaps. Transferring BTC from Binance to your Ledger is NOT a sale.

3. Using incorrect market prices or acquisition dates. A date error can completely alter FIFO calculations.

4. Not declaring staking, airdrop, or farming rewards. These are considered investment income.

5. Ignoring transaction fees when calculating gains or losses. Gas fees reduce your capital gain.

6. Submitting automatic reports without manual data review or with tokens unrecognized by the AEAT. Automated tools often make mistakes.

Real Example of a Common Error

Typical case:

An investor buys 1 ETH on Coinbase for €2,000, transfers it to their MetaMask wallet (pays €15 gas), then swaps it for 50 XYZ tokens on Uniswap (pays €20 gas), and finally sells the 50 XYZ for €2,500 on another exchange.

Frequent mistake:

Declaring only the final sale of €2,500 without considering:

• The initial acquisition cost (€2,000)
• The gas fees (€35 total)
• The ETH → XYZ swap as a taxable event

Correct declaration:

1. First operation: ETH → XYZ

   • ETH cost: €2,015 (€2,000 + €15 gas)
   • XYZ value received: €1,980 (market value at the time of swap)
   • Loss: -€35

2. Second operation: Sale of XYZ

   • Cost: €2,000 (€1,980 + €20 gas)
   • Sale: €2,500
   • Gain: €500

Total capital gain: €465 (500 - 35)

An incorrect report can lead to:

• Financial penalties: From 50% to 150% of the undeclared amount
• Late filing surcharges: From 5% to 20% depending on the delay
• Requests for additional information: The tax agency may request supporting documents for all your transactions
• Tax audits: In cases of major or repeated discrepancies
• Interest charges: Applied to unpaid amounts

Calculation errors or omitted transactions are usually easily detected by the tax authorities thanks to data cross-checks with both domestic and international exchanges.

Important: The AEAT receives information from exchanges such as Coinbase, Binance, and Kraken, among others operating in Spain. Discrepancies between your declaration and AEAT data trigger automatic alerts.

Additionally, repeated errors may be considered negligence or tax fraud, significantly increasing the amount of penalties. That’s why it’s essential to file a complete, consistent, and verified tax report.

The key is to work with organized data, accurate market prices, and up-to-date tax criteria.

Checklist Before Generating Your Tax Report:

• ✅ Gather all transactions from all exchanges and wallets
• ✅ Identify internal transfers vs. taxable operations
• ✅ Classify each transaction correctly (buy, sell, swap, staking, etc.)
• ✅ Verify historical market prices for every transaction
• ✅ Apply FIFO correctly to calculate gains and losses
• ✅ Include all fees (gas fees, trading fees, etc.)
• ✅ Review tokens without market value or with incomplete data
• ✅ Validate consistency across different platforms

Before generating your tax report, ensure all movements are correctly classified (purchases, sales, swaps, yields, etc.).

At Cleriontax, we review every operation, identify inconsistencies, and correct data errors to produce an accurate and traceable tax report validated under current regulations.

Our Validation Process Includes:

1. Initial automated analysis of all transactions
2. Anomaly detection (out-of-range prices, duplicates, etc.)
3. Manual review by specialized tax advisors
4. Accurate tax classification of each transaction type
5. Cross-validation across multiple data sources
6. Generation of the final report ready for inclusion in your tax return

If you detect an error in a previous tax return, don’t wait for the tax agency to notify you. You can file:

Complementary Declaration

If you discover omitted transactions or income resulting in a higher tax liability:

• It can be filed at any time
• Includes surcharge and late payment interest
• The surcharge is lower if filed voluntarily (from 5% to 20%)

Corrective Declaration (Request for Amendment)

If you discover that you overpaid or made errors not resulting in additional tax owed:

• Must be submitted before the statute of limitations expires (usually 4 years)
• The tax agency may refund overpaid amounts
• No surcharges or penalties apply

The key is to act before receiving a tax notice. Voluntary submission significantly reduces penalties.

Our team can help you:

• Review and analyze your previous declaration
• Identify specific errors
• Rebuild the tax report correctly
• Prepare the complementary or corrective declaration
• Guide you through the entire process

This reduces the risk of penalties and demonstrates good faith to the AEAT.

Declaring cryptocurrencies correctly requires more than an automatic file: it demands tax expertise, data validation, and full traceability.

Avoiding mistakes not only saves you from penalties, but also:

• Demonstrates compliance and transparency to the tax authorities
• Optimizes your tax situation by paying exactly what you owe
• Prevents future audits and sanction procedures
• Ensures asset security with complete documentation

The difference between an automatic and a professionally reviewed report can mean thousands of euros in avoided penalties and peace of mind.

At Cleriontax, we don’t just generate tax reports — we validate and verify them to ensure every data point is correct and every operation properly classified.

Our commitment:

• ✅ Manual review of all data by certified tax advisors
• ✅ Detection and correction of errors before report generation
• ✅ Correct application of FIFO and updated tax criteria
• ✅ Traceable reports backed by full documentation
• ✅ Support in case of AEAT inquiries

Request a Review of Your Tax Report → →

Contact our team for a free initial assessment. We’ll explain exactly what you need to do and how we can help you correctly declare your cryptocurrencies.

Disclaimer: This article is for informational and educational purposes only. It does not constitute personalized tax advice or investment recommendations. Tax regulations are subject to change, and each personal situation is unique. Always consult a certified tax advisor for your specific case.

Last updated: October 2025

Published by: Cleriontax Team – Experts in Cryptocurrency Taxation and Data Analysis